138 Illinois State Laboratory of Natural History. 



The antepenultimate article of the prehensile antenna (PL 

 XXIII., Fig. 6-8) is not so variable, but still quite a differ- 

 ence may be noted in the width of the hyaline plate and in 

 the relative lengths of the segments. 



In the female the variation in size is even greater than 

 in the male, the fifth legs being shown in PL XXV., Fig. 1, 2. 

 The variation in the "hump" of the female is slight (PL 

 XXIV., Fig. 5, 6), as is also that of the first abdominal seg- 

 ment (PL XXIV., Fig. 1, 2). 



While I have found no variation whatever in the color of 

 D. sanguineus, all of the specimens I have seen alive being a 

 bright uniform red, as were also those examined by Dr. 

 Forbes (76), and by Gissler ('81), Gissler later ('81a) found 

 individuals colored as follows : body and legs bluish, an- 

 tenna? and furca red, and abdomen yellow. Herrick says 

 in the description of D.minnetonka (Herrick and Turner, '95), 

 which is a synonym of D. sanguineus, "color dark." In the 

 same work, in his description of D. sanguineus, he says 

 "brilliantly colored." According to my observation color is 

 of no certain specific value in Diaptomus, but it may be that 

 there are definite seasonal variations — a subject which I have 

 not investigated. 



Diaptomus stagnalis Forbes. (PL XXVIII., Fig. 2.) 



Diaptomus stagnalis, Forbes, '82a, p. 646, PL VIII., Fig. 8, 10-12, 14. 

 Diaptomus giganteus, Herriek,'82,p. 222, PI. II., Fig. 3, 11, 15. 

 Diaptomus stagnalis, Herrick. "84, p. 139, PI. Q, Fig. 11, 13. 

 Diaptomus stagnalis, de Guerne et Richard, '89b, p. 23, PI. IV.. Fig. 14. 



Head distinct from thorax; fifth and sixth thoracic seg- 

 ments confluent. Lateral angles of last thoracic segment 

 strongly produced backward, each angle bilobed, the outer 

 lobe about twice as large as the inner; (in the male this seg- 

 ment is salient.) Abdomen peculiar in that there is a sudden 

 narrowing at the beginning of the third segment. First 

 abdominal segment armed with a large spine on each side 

 (in the male unarmed) ; second and third segments of the 

 abdomen subequal, about twice as wide as long. Furcal 

 rami subquadnite, hairy within. Furcal seta rather short, 



